Spark ignited engines, such as are used in motor vehicles, are provided with a plurality of spark plugs for the ignition of combustion in their combustion chambers and one or more ignition coils for the generation of a high voltage to initiate sparks in the spark plugs. The high voltage ignition pulses are conducted from an ignition coil to one or more spark plugs over high voltage ignition wires having a connector at one end for the ignition coil and at the other end for the spark plug.
The connector at the ignition coil end of the ignition wire is a right angle, female connector which is pushed, typically downward, over a terminal post extending typically upward from the ignition coil. In the case of a four cylinder engine, for example, in which two spark plugs are simultaneously sparked by a single coil, an ignition coil may have two such terminal posts extending upwards parallel with each other at a predetermined horizontal separation, one for each of the two spark plugs that are to be simultaneously sparked.
In an engine ignition system assembly, each ignition wire must be installed on an ignition coil by means of the connector being pressed downward over the terminal post, with sufficient force that retention apparatus within the connector is activated to its connector retaining condition. This action requires significant force, since the retention apparatus is designed to hold a connection for a long time in an environment characterized by significant temperature swings and physical vibration. If such a connector is not pressed downward a sufficient distance over the terminal post (or with sufficient force), or if the connector is not kept straight while it is being pressed, the internal retention apparatus might not be fully activated; and the connector may come loose after the engine is put in service. But it is also desired to avoid repetitive stress injuries to those who install ignition wires repetitively on ignition coils in the engine assembly process.